Print Full Reverse K Star Pattern in Java

Pattern Printing Programs

Topic

In this article, we will learn how to print a Full Reverse K Star Pattern in Java. This pattern consists of two joined triangle shapes—one decreasing and one increasing—with a center line of a single star. It visually resembles a mirror image of the letter 'K' and is a great exercise in loop control and symmetry logic.

To build this, we use:

  • for loops for rows and columns
  • Nested loops to print spaces and stars
  • Simple conditional logic to decide how many stars and spaces to print per row

Examples

Input: n = 5

*****
 ****
  ***
   **
    *
   **
  ***
 ****
*****

Input: n = 3

***
 **
  *
 **
***

Input: n = 1

*

Interviewer Expectations

The interviewer wants to evaluate your understanding of:

  • Looping constructs like for loops
  • Printing patterns using nested loops
  • Managing spaces and alignment
  • Clean code and logical problem solving

Approach

The pattern is divided into two halves:

  • Top half (including middle line): Decreasing triangle with increasing spaces
  • Bottom half: Increasing triangle with decreasing spaces

For the top half (rows 1 to n):

  • Print i - 1 spaces
  • Print n - i + 1 stars

For the bottom half (rows 1 to n - 1):

  • Print n - i - 1 spaces
  • Print i + 1 stars

Dry Run (n = 3)


Top Half:
Row 1: spaces = 0, stars = 3 → ***
Row 2: spaces = 1, stars = 2 →  **
Row 3: spaces = 2, stars = 1 →   *

Bottom Half:
Row 1: spaces = 1, stars = 2 →  **
Row 2: spaces = 0, stars = 3 → ***

Java Program

public class ReverseKFullPattern {
  public static void main(String[] args) {
    int n = 5;

    // Top half
    for (int i = 1; i <= n; i++) {
      for (int space = 1; space < i; space++) {
        System.out.print(" ");
      }
      for (int star = 1; star <= n - i + 1; star++) {
        System.out.print("*");
      }
      System.out.println();
    }

    // Bottom half
    for (int i = 1; i < n; i++) {
      for (int space = 1; space < n - i; space++) {
        System.out.print(" ");
      }
      for (int star = 1; star <= i + 1; star++) {
        System.out.print("*");
      }
      System.out.println();
    }
  }
}
*****
 ****
  ***
   **
    *
   **
  ***
 ****
*****

Possible Followup Questions with Answers

1. How do you make the pattern right-aligned?

By printing the correct number of spaces before stars using nested loops.

2. How to accept user input for number of rows?

Scanner sc = new Scanner(System.in);
int n = sc.nextInt();

3. What is the total number of rows in the pattern?

The pattern has 2 * n - 1 rows (top half + bottom half excluding the center repeated).

4. Can this be done with a single loop?

Not efficiently. The pattern requires careful handling of two different shapes, so separate loops improve readability and logic clarity.


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